Guidance for Determining Homogeneous Materials in the
Cradle to Cradle Certified™ Product Standard
Version 1.0
March 2016
© Copyright, Cradle to Cradle Products Innovation Institute, 2016
No part of this publication is to be reproduced or utilized in any form or by any means, without
prior written permission from the Cradle to Cradle Products Innovation Institute.
Cradle to Cradle Certified™ is a certification mark exclusively licensed by the Cradle to Cradle
Products Innovation Institute.
TABLE OF CONTENTS
GUIDANCE FOR DETERMINING HOMOGENEOUS MATERIALS IN THE CRADLE TO
CRADLE CERTIFIED™ PRODUCT STANDARD REVISION HISTORY .................................. II
1 OVERVIEW ................................................................................................................. 1
1.1 Purpose and Content................................................................................................................... 1
1.2 Supporting Documents ................................................................................................................ 1
2
3
HOMOGENEOUS MATERIAL DEFINITION AND GENERAL GUIDANCE .................... 2
2.1 Definition ........................................................................................................................................ 2
2.2 Scope ............................................................................................................................................. 3
INTERPRETATIONS BY PRODUCT TYPE ...................................................................... 3
GUIDANCE FOR DETERMINING HOMOGENEOUS MATERIALS
i
GUIDANCE FOR DETERMINING HOMOGENEOUS MATERIALS IN
THE CRADLE TO CRADLE CERTIFIED™ PRODUCT
STANDARD REVISION HISTORY
REVISION
1.0
ii
SECTION TYPE OF CHANGE
Initial Release
DATE
03/2016
AUTHORIZED BY
S. Klosterhaus
1 OVERVIEW
1.1 PURPOSE AND CONTENT
This document explains how to determine a product’s homogeneous materials for the purposes of
applying the requirements in the Cradle to Cradle Certified™ Product Standard. Homogeneous
materials are referenced in several requirements, summarized below:
•
With some exceptions, homogeneous materials present in a product at weight fractions of 100
ppm or greater are subject to review.
•
With some exceptions, chemical substances present in any of those homogeneous materials
at 100 ppm or greater are subject to review.
•
Banned list substances must not be present above designated thresholds in any of a product’s
homogeneous materials that are subject to review.
•
For most products, the percentage assessed refers to the percentage of homogeneous
materials that have been assessed.
•
Each of a product’s homogeneous materials is designated as a biological or technical nutrient.
•
Recyclability is determined at the homogeneous material level.
The purpose of clarifying the homogeneous material definition is to improve consistency among
assessments, as comparable products should be assessed in the same way regardless of the
assessment body completing the work.
This document includes the homogeneous material definition and general guidance, as well as a set of
interpretations indicating how the definition has been applied in ambiguous or borderline cases in the
past. Assessors must apply these interpretations to their future work and contact the Institute
([email protected]) when assessing products with ambiguous homogenous material
breakdown that do not yet appear in the list of interpretations. This document will be updated
regularly to reflect such additions.
1.2 SUPPORTING DOCUMENTS
The following documents are to be used in conjunction with this guidance document:
● Cradle to Cradle Certified™ Product Standard
● Any additional supporting documents and guidance posted on the C2CPII website
GUIDANCE FOR DETERMINING HOMOGENEOUS MATERIALS
1
Visit the Cradle to Cradle Products Innovation Institute website to download the Standard documents
and obtain the most current information regarding the product Standard
(http://www.c2ccertified.org/product_certification/c2ccertified_product_standard).
2 HOMOGENEOUS MATERIAL
DEFINITION AND GENERAL
GUIDANCE
2.1 DEFINITION
Homogeneous materials are defined in the Standard as follows:
Homogeneous materials are defined as materials of uniform composition throughout that cannot
be mechanically disjointed, in principle, into different materials. Examples of homogeneous
materials are polypropylene, steel, shampoo, glass cleaner, nylon yarn, finish, and coating.
Examples of non-homogeneous materials are powder-coated steel, a printed bottle label,
plywood, laminate, and chair casters.
The definition is based on the one used in the European Union’s Restriction of Hazardous Substances
(RoHS) legislation, which provides some additional context:
‘homogeneous material’ means one material of uniform composition throughout or a material,
consisting of a combination of materials, that cannot be disjointed or separated into different
materials by mechanical actions such as unscrewing, cutting, crushing, grinding and abrasive
processes.1
Thus, a homogenous material does not necessarily possess uniform composition throughout, as long
as the scale, structure, or distribution of the domains with differing composition do not allow for these
domains to be separated from one another through mechanical means. Homogenous materials may
be homogenous as viewed by the naked eye, but heterogeneous at a microscale.
Accordingly, assessors applying the definition to their projects must consider whether it would be
possible to mechanically separate materials using one or more of these mechanical actions, regardless
of whether the materials are likely to be separated in practice. For example, most layered products and
coated products consist of multiple homogeneous materials because the layers/coatings could be
separated, in principle, by sanding, even if this is not likely to occur.
While coated products are often more than one homogeneous material, this is not always the case
because the scale of the substrate must be considered when determining whether the substrate and
1
European Commission. Directive 2011/65/EU of the European Parliament and of the Council of 8 June 2011 on the restriction of the use of
certain hazardous substances in electrical and electronic equipment (recast). 2015. http://eur-lex.europa.eu/legalcontent/EN/TXT/HTML/?uri=CELEX:02011L0065-20150624&from=EN.
2
GUIDANCE FOR DETERMINING HOMOGENEOUS MATERIALS
coating are separable. For example, a painted wooden table leg is considered two homogeneous
materials because the paint could be sanded off, but a polyester fabric coated with liquid latex in
conventional carpet construction is considered one homogeneous material because the latex will
infuse the fabric surrounding individual threads in a way that makes it impossible to separate them
from the latex matrix through mechanical means. Similarly, coated fiberglass is considered a
homogenous material since individually coated fibers are too small to manipulate and remove the
coating from through mechanical processes.
2.2 SCOPE
The Standard requirements pertain to the homogeneous materials in the finished product, rather than
the homogeneous materials the applicant receives from suppliers and combines during the
manufacturing process. For example, if the product under review is dyed fabric, the dyed fabric is a
single homogeneous material, even though the dye and the fabric were separate homogeneous
materials when purchased from suppliers.
3 INTERPRETATIONS BY PRODUCT
TYPE
In some cases, the appropriate way of separating a product into homogeneous materials according to
the definition and guidance in section 3 is unclear. To achieve greater clarity, the following table
explains how to apply this definition to a variety of ambiguous cases.
Product Type
Homogeneous Materials Interpretation
Blended textiles (more than
one thread or yarn type
woven together)
Each yarn or thread type is its own homogeneous material. For
example, if a fabric is composed of a polyester yarn and a cotton yarn
woven together, the polyester and cotton are considered separate
homogeneous materials (in principle, individual yarns could be
physically separated from the fabric, e.g. by pulling them out one at a
time).
If fibers of different types are twisted together into yarn or different
types of yarn are twisted together in a multi-ply yarn or thread, the
resulting multi-ply yarn or thread is one homogeneous material,
because the different fibers are not separable by any mechanical
process.
Carpet backing
The primary backing fiber and precoat are considered the same
GUIDANCE FOR DETERMINING HOMOGENEOUS MATERIALS
3
homogeneous material because the primary backing fiber becomes
permeated by the precoat during the manufacturing process and is
thus embedded within a precoat matrix in the finished product.
The secondary backing is considered a separate homogeneous
material.
Composite wood products
Layered composite wood products (e.g. plywood) are considered
more than one homogeneous material (each layer is a homogeneous
material).
Non-layered composite wood materials such as MDF or particle
board, in which small wood particles or fibers are uniformly
distributed within a binder matrix, are regarded a single
homogeneous material. However, if such a material has a surface
layers or coating (such as a veneer, varnish, or paint) then that
surface layer or coating counts as a separate homogenous material.
Concrete, countertops made
of glass and cement, and
other mixtures of cement
with structural or decorative
rock or silica-based
inclusions
Any mixture of cement, admixture, and/or rock or silica-based
inclusions is regarded a homogenous material regardless of the size
of the inclusions. While gravel and similar sizes inclusions could in
principle be separated from the matrix through mechanical means,
analogous geological materials (i.e. conglomerates) are treated as
homogenous materials for the purpose of assessment. Additionally,
assessing types of concrete differently based on aggregate size
would greatly increase the challenge of ensuring consistent
application of the homogenous material definition.
Dyed textiles
Dyes and their substrates usually form a single homogeneous
material, though if the dyes are surface treatments only, they can be
counted as separate homogeneous materials from their substrates.
For example, if a pattern is printed onto a fabric, the print is
considered a separate homogeneous material from the fabric
because it is resting on top of the fabric as a distinct layer that could
be separated through abrasion. If the dyes instead form a single
homogeneous material with their substrate (this is the more
common situation), then each colored fabric option (e.g. blue fabric,
purple fabric, green fabric) is its own homogeneous material.
Fiberglass
4
Fiberglass is considered a single homogeneous material. While the
glass fibers may be coated, and therefore the composition may not
be uniform throughout at the scale of an individual fiber, the glass
and coating are not separable by any mechanical process.
GUIDANCE FOR DETERMINING HOMOGENEOUS MATERIALS